TSW reduced by kaolin coat

It only takes a few minutes of feeding for thrips to transmit the virus that causes tomato spotted wilt disease (TSW), despite growers’ attempts to prevent such assaults with insecticide spraying.

But thrips are highly visual insects, and scientists with the Agricultural Research Service (ARS) and University of Florida (UF) are exploiting that dependency to, in effect, camouflage the tomato plants. In field trials, the scientists sprayed the plants with kaolin, a type of powdered clay, and one of three plant essential oils that together reduced the incidence of TSW by 50 percent.

According to Stuart Reitz, an entomologist with the ARS Insect Behavior and Biocontrol Research Unit’s Tallahassee, Fla., site, kaolin forms a white coat that may interfere with thrips’ ability to zero in on color cues during flight. Thrips that do still land on treated plants may find the kaolin coat difficult to penetrate with their juice-sucking mouthparts. This, in turn, may diminish their transmission of the TSW virus, which is present in the insects’ saliva.

Used alone, kaolin diminished TSW on experimental plots of tomato by 33 percent. Combining it with tea-tree oil, lemongrass oil or geraniol reduced the disease further by 17 percent, reports Reitz. His collaborators are UF plant pathologist Timur Momol and Steve Olson at the university’s North Florida Research and Education Center at Quincy.

In northern Florida, commercial growers have scored some success against thrips by using ultraviolet-light-reflective mulches. But for small-operation growers, such mulches may be too costly, leading Reitz and colleagues to explore kaolin and essential oils as less expensive commercial alternatives.

Severe outbreaks of thrips and TSW can cause yield losses of 100 percent. Once infected, the plants cannot be cured. But in a complementary approach, the ARS-UF team has begun field testing kaolin and essential oils plus acibenzolar-s-methyl, a commercial product that stimulates natural plant defense mechanisms, potentially containing the TSW virus and limiting its spread.